Something Cool You May Not Know About Water

When I was a kid I used to play with Star Wars action figures. I’d imagine battles and stories and play them out with my range of characters (and being a kid and therefore inherently evil the bad guys would usually win). Anyway, my parents used to have a large chest freezer and some days I’d take my Han Solo character and freeze him in ice – pretending it was like the carbonite in The Empire Strikes Back and Return of the Jedi.

Being a nerdy young lad I wanted to try and re-create that authentic look so tried freezing him in Coke – which is black like the carbonite from the film. Sadly rather than the jet black effect it pretty much ended up looking like regular ice with a bit of slush on the surface. Lesson learned – don’t waste Coke by freezing it, just drink the stuff.

I once froze him submerged in a glass jam jar just for fun. Unfortunately I then discovered the interesting fact that when water freezes it expands as the jam jar had cracked into several pieces in the freezer. (I didn’t mention this to my parents). Lesson learned.

In the end I found that if I put him in a shallow plastic container on his back (a small Tupperware would do) then I could recreate the Return of the Jedi frozen Han Solo look after a few hours in the freezer. I could then carry on playing and act out a rescue scene where the villains let him think he’s getting away and kill him at the last minute (because the bad guys always win).

Anyway, I froze him quite a number of times, thawed him out in a rescue attempt and froze him again for the next chapter. Once, out of curiosity, I put warm water in the container instead of cold. I imagined that the small quantity of warm water would defrost the entire freezer and spoil all the food therein. I was quite wrong (sadly) and even more surprisingly the water actually seemed to freeze quicker than it normally did (being a very impatient child I’d check on the freezing process many times until it was done). Since it made no sense at all that warm water would freeze faster than cold I just thought I was mistaken and carried on playing.

But you know what? Believe it or not – and I’m pretty sure you won’t – warm water DOES freeze faster than cold water. It goes against all rational thinking, but it’s absolutely true!

First described by Aristotle back in 350BC, this curious effect had long been forgotten until it was re-discovered in the 1960’s and called the Mpemba effect after the youngster who came across it. I read about this phenomenon from a book called, I kid you not: “How to Fossilise Your Hamster: And Other Amazing Experiments For The Armchair Scientist” (pictured right). It’s published by New Scientist and is filled with interesting experiments you can do at home including demonstrating that hot water can freeze faster than cold (the optimal test is to fill two ice cube trays with water, one at 5ºC and the other at 35ºC and put them in the freezer – you’ll find the latter freezes first even though the former reaches 0ºC first).

The even more curious thing about hot water freezing faster than cold water is that there’s no scientific explanation as to why. There are plenty of theories (and no, it’s not because the thermostat in your freezer goes into overdrive as the water is hot making it cool faster – you can do this outside if your Winter climate is cold enough and the same thing still happens) but none that have been unequivocally proven to be correct. Can you think of a reason?

It just goes to show that even in the 21st century with all our miracles of modern technology that something as seemingly inert and simple as water can be shrouded in mystery. Now, time to head to the pet shop for a hamster to fossilise… 😉

Hmmm, I’m not sure. I think I need to repeat the experiment again and look more closely! The book mentions several theories including the following:

“The rate of heat loss from the upper surface is proportional to the temperature of the surface. So if the surface can be kept at a higher temperature than the bulk of the remaining liquid (in this case, the initially warmer water), then the rate of heat loss will be greater than from liquid with the same average temperature uniformly distributed (in this case the initially cooler water).”

Its almost like some sort of thermal momentum, because the hot water has to cool more than the lower temperature water, once it does start to freeze it does so at a faster rate…rubbish I know!
I guess its like alot of things in physics, if you put together things at opposing ends of their respective states, then you get the most dynamic reaction.
Oddly enough, when making ice-slides on the pavement as a kid we found that chucking warm water on the ground gave a much more ‘glassy’ grade of ice than cold water, which usually went frosty, not icy. Now I know its because the hot water froze faster…thanks for clearing that up John! ;o)

You’re most welcome Phil! Interesting about the glassy grade of ice, when I decide to try and kill off the missus for the insurance I’ll bear that in mind when setting up the trap at the top of some steps! 😉

That’s interesting Melanie, so I guess it’s a well known fact in colder climates.

I didn’t have a Princess Leia I’m afraid, I tended to go for all the villains rather than the good guys. This was of course before I was old enough to be attracted to women so my collection was filled with men in uniform instead! Eek!

I did have an R2-D2, but it was an airfix model that was about a foot high if I remember correctly! I had more figures but looking at them they really were almost exclusively the bad guys. I didn’t even have a wookie!

UUMMMMMMMMMMMMMMMMMMMMM, TREKIES……..THE TEMPERATURE FALLING IS NOT LIKE A HIGH JUMP, WHERE A GOOD RUNNING START HAS INERTIA TO CARRY YOU OVER THE TOP. FAST HEAT LOSS INITIALLY WILL SLOW TO SAME RATE OF THE OTHER WATER WHEN IT REACHES THAT TEMPERATURE….DON’T APPLY YOUR PHYSICS TO YOUR BOOSTER ROCKETS EITHER.

Secondly, you’re not clear if you’re agreeing with or disagreeing with the fact (and it is a fact) that 35ºC water freezes faster than water at 5ºC. While the 5ºC water reaches 0ºC faster than the water at 35ºC (obviously), it’s the initially-warmer water that solidifies first and you can try it under laboratory conditions yourself to confirm that’s the case. The rate at which the water cools until it hits 0ºC is generally uniform, it’s when it hits the magic 0 that things go strange. Not sure what the relevance is to booster rockets – I’ll leave that to the experts!

FRANK also called you trekkies when you’re discussing star wars, which just goes to show exactly how little attention he was paying. I did not know that warm water froze quicker … have you done any experiments to see if it continues up the scale (i.e. does 80C water freeze quicker than 60C water and so on down), or if there’s an optimal temperature at which to put water in an ice cube tray? I’m thinking this could be very useful information for any spontaneous drinkies that might occur in a household short on ice cubes …